1. Field of the Invention
The present invention relates generally to a viscous fluid coupling device. In particular, the present invention is concerned with an integrally formed wiper and orifice for a pump plate of a viscous fluid fan clutch.
2. Statement of the Related Art
A thermostatically-controlled viscous fluid clutch assembly for driving and rotating a vehicle cooling fan is well-known. A multi-bladed fan is removably secured to a body of the clutch assembly. The fan and clutch assembly are installed between an accessory pulley of a vehicle engine (typically the water pump pulley) and a radiator. The clutch assembly drives the fan at high speeds close to input speed when cooling is required and permits the fan to rotate at low speeds when cooling is not required. Thermostatic control of the fan through the clutch assembly reduces the load on an engine and the noise caused by fan rotation, resulting in horsepower gain and improved fuel economy.
Generally, a clutch assembly includes a clutch plate having lands and grooves mated to the body having complementary lands and grooves. A pump plate separates a pair of internally-contained chambers, a collecting chamber and a pumping chamber, from a reservoir. Gates in the pump plate permit selective flow of a viscous fluid from the reservoir to the collecting chamber and into a shear zone between the lands and grooves of the body and clutch plate. Fluid sheared between the lands and grooves transfers input torque from the clutch plate to drive the body and the attached fan.
When cooling is not required, gates in the pump plate are closed and the fluid in the shear zone is pumped into the pumping chamber. Orifices in the pump plate permit passage of the fluid from the pumping chamber into the reservoir. The removal of a majority of the fluid from the shear zone substantially reduces the shear between the clutch plate and the body, thereby substantially reducing the rotation of the fan.
It is well-known to provide wiper elements on a surface of the pump plate in communication with the pumping chamber. A wiper, which can be formed as a thin, flat element, is secured to the pump plate (usually by welding) adjacent each pump plate orifice. In other embodiments, a wiper may be integrally formed with the pump plate by stamping a cylindrical projection in a pump plate adjacent each pump plate orifice. As the wiper encounters fluid in the pumping chamber, an increase in fluid pressure in the pumping chamber occurs as the wiper creates a fluid dam. The increase in fluid pressure results in increased fluid flow through the pump plate orifices.
To further enhance the pumping ability of a wiper, it is well-known to provide a "scoop" surface on a wiper. A scoop surface is a curved surface of the wiper oriented toward a pump plate orifice. A curved surface may include an inlet or "bay" portion which receives oncoming fluid in the pumping chamber and creates a fluid dam.
A welded wiper is generally more costly than a wiper formed through a stamping operation because of the additional assembly time. However, scoop surfaces provided in welded wipers provide increased pump-out capabilities over conventional stamped wipers which do not include scoop surfaces. With both welded and stamped wipers, an orifice must be provided in the pump plate adjacent each wiper.
The art continues to seek improvements. It is desirable to provide wipers on a pump plate to provide quick pump-out of fluid in a pumping chamber. Furthermore, it is desirable to provide a low-cost stamped wiper having a fluid damming surface which is economical to manufacture and compatible with conventional pump plates.